Acylation of refined wood pulp



United tates Patent flee ACYLATION F REFINED WOOD PULP Kenneth Russell Gray, Judson Harry Holloway, and Bel-Wyn Brainerd Thomas, Shelton, Wash, assignors t0 Rayonier Incorporated, Shelton, Wash, a corporation of Delaware No Drawing. Application May 3, 1951, Serial No. 224,446

16 Claims, (Cl. 260-212) This invention relates to the production of cellulosic products and has for its general object the provision of certain improvements in carrying out one or more of the processing steps used in the production of such products. The invention aims particularly to minimize inactivation efiects in the production of a substantially dry sheet of refined wood pulp from a slurry of Wet fibers. The invention further contemplates, as a new article of manufacture, substantially dry refined wood pulp in sheet form having incorporated therein a glycol ether compound of relatively low molecular weight.

In. one of its further aspects, the invention involves the use of substantially dry refined wood pulp. as a source of cellulose in the preparation of cellulosic derivatives. The invention aims particularly to improve the completeness of acylation of a substantially dry refined Wood pulp in sheet form, and contemplates use in acylation processes of substantially dry refined Wood pulp in sheet form having certain glycol ether compounds incorporated therein prior to completion of drying at an elevated temperature, whereby inactivation of the. pulp as regards production of cellulosic esters is minimized.

The invention further contemplates use of the dry treated pulp in aqueous conversion processes wherein dry sheet pulp is steeped in aqueous caustic soda of mercerizing strength, whereby the rapidity and completeness of mercerization are improved. This improvement in mercerization results in further improvements when the .alkali cellulose. so produced is utilized in the production of other cellulose derivatives (e. g. cellulose Xanthate). As used in this specification substantially dry refers to pulp either dried bone dry or containing that small moisture content which pulp being a hygroscopic substance would take up from the air. Roughly this will refer to pulp containing from zero to ten percent moisture.

In the preparation of sheets of refined wood pulp, the purified fibers are first obtained in the form of a slurry in. water. In this undried state, the refined wood pulp fibers are potentially very reactive, since it the water in the. wet fibers is first displaced by organic solvents, the fibers reacting rapidly in nonaqueous processes. such. as .the production of cellulose acetate.

Again in conversion processes taking place in an aqueous medium, such as the conversion to cellulose Xanthate in the viscose process, the wet fibers may be very readily converted by treatment in slurry form without drying.

For practical reasons, however, it is generally necessary to formthe pulp fibers into a dry pulp sheet, using heat to remove practically all the water. In such dry sheet form, the pulp may be readily shipped to distant factories for conversion into various derivatives. Also, in such relatively dry form, the pulp may be used in non-aqueous conversion processes without the need for expensive dis.- placement of water by organic solvents.

However, in the formation of the pulp sheet and the drying at elevated temperature, the pulp fibers undergo various degrees of inactivation.

As regards use in the cellulose acetate process, such Fatented Oct. 16, 1956 in inactivation efiects probably result largely from the drying at elevated temperature. As regards use in conversion processes taking place in aqueous media, inactivation is often less marked and is possibly due in large part to mechanical effects of sheet formation.

We have discovered novel agents which, when added to the pulp in minute quantities prior to completion of drying, greatly minimize inactivation efiects due to the production of a dry pulp sheet from the wet fiber slurry. The agents of our invention minimize both the inactivity primarily due to heat as regards use in cellulose acetate formation and that inactivity due to sheet formation as regards use in aqueous conversion processes (e. g, formation of alkali cellulose in the viscose process).

In. accordance with the invention a small quantity O a glycol ether of types hereinafter described is incorporated in the pulp prior to completion of drying the pulp sheet at an. elevated temperature. These compounds which we have discovered for use in the invention are very efiective in preventing loss of reactivity of the fibers during the drying of the pulp and accordingly can be used in very small quantities. As applied to the production of a substantially dry sheet of pulp, the invention involves carrying out the drying of the sheet or at least the final stage of drying in the presence of said glycol ethers.

The treated pulp of our invention containing the glycol ethers may be used with particular advantages in the production of cellulose acetate. The treated pulp, however, may also be used for the production of other cellulose derivatives such as cellulose Xanthate in the viscose process.

The compounds used in the pulp treating and improved acylation processes of the invention are glycol ether compounds having the formula where R is a hydrocarbon radical selected fromthe group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and where x is an integer from 1 to 2.

In general the glycol ether compounds of the invention are liquid, water-soluble, mixed ethers of relatively high boiling point. These mixed ethers are monoethers of diethylene glycol or ethylene glycol which contain a relatively small hydrocarbon radical. Specifically, the mixed ethers are monoethers of ethylene glycol or diethylene glycol with an aliphatic alcohol having from 1 to 6 carbon atoms or With phenol or benzyl alcohol.

The aliphatic alcohols used in these mixed ethers may be either straight or branched chain, saturated or'unsaturated. In most cases, however, the alkyl radicals will be saturated.

It is to be noted that the hydrocarbon radicals in the mixed ethers of our invention are definitely smaller than the hydrocarbon radicals normally considered as having suficient lipophilic properties to induce surface activity in conventional surface-active agents. The mixed ethers further differ from compounds normally considered surface-active agents in that they are of relatively small molecular Weight and form true solutions in water;

In addition to being soluble in water, the agents of the invention have marked afiinity for organic compounds and are miscible with many organic solvents.

For use in treating pulp the ethers of diethylene glycol are preferred over the ethers of ethylene glycol both from the standpoint of lesser volatility and from the standpoint of eifectiveness. V

Typical members of the glycol ethers are manufactured commercially for use as high boiling solvents. The compounds can be prepared irom ethylene oxide by using surfaces of V the sheet.

3 a the appropriate alcohol for the alkylatiug agent and the reaction may be expressed as follows:

The appropriate alcohol in water-free condition and ethylene oxide are heated together in an autoclave at an elevated temperature. After discharging the autoclave, the products may be separated by fractional dis-. tillation. In general corresponding mixed ethers of ethylene glycol and diethylene glycol may be formed simultaneously together'with smaller amounts of mixed ethers of polyglycols higher than diethylene glycol.

While purified products separated from the reaction mixtures by distillation are very suitable for use in the invention, it is also possible to obtain'the advantages of theinvention by use of the reaction mixture itself containing substantial quantities of monoethers of ethylene glycol and diethylene glycol, and small amounts of monoethers of higher glycols. Where-such a reaction mixture is used without purification by distillation, it will be desirable to first neutralize any residual alkalinity from any alkali used in catalyzing the reaction. The following glycol ether compounds are examples of comp unds which may be used in our invention:

Diethylene glycol ethers of:

.hexyl (Z-ethyl butyl) alcohol n-butyl alcohol ethylalcohol 'methyl'alcohol.

Ethylene glycol monoethers of: hexyl (Z-ethyl butyl) alcohol n-butyl alcohol ethyl alcohol methyl alcohol a phenol benzyl alcohol The glycol ether compounds maybe incorporated in the wood pulp at any stage in the production of dry sheet pulp from theiwet fiber slurry. For treating the pulp, the compounds may be incorporated either in the bulk pulp before sheet formation or in the sheet at any stage of the drying as by spraying the pulp with an aqueous solution or. dispersion. A most practical and convenient method of securing the incorporation of the glycol ethers prior to completion of drying is to incorporate them in the refined wood pulp while it is on the sheet forming machine by means of sprays or arotating roll.' Such application may be made to the wet pulp web subsequent to removal of the mechanically removable water by pressing, or later at any stage while it is passing through the hot dryer rolls prior to completion of drying.

When pulp is dried in a conventional manner on hot dryer rolls, inactivation of the fibers is greatest on the surface of the sheets. The inactivation probably results from minute changes in physical structure of thefibers, as for. example in hydrogen bonding, caused by loss of the last portions of Water under conditions of high temperature. It is the function of the added compounds of the invention to prevent or minimize these physical' changes and thus prevent or minimize inactivation. Thus, if desired, the treatment of the pulp sheet with the agents of the invention may be accomplished with a spray or a rotating roll in such a manner-that the glycol ether compounds are largely' incorporated near one or both to those fibers which would'othe rwise have the greatest tendency toward inactivation. Inlany event there i produced a substantially dry sheet of pulp containing a glycol ether compound incorporated prior to completion of drying.

While the invention will be most usually applied insheet pulp will have at least one or both surfaces treated with a water solution of a mixed ether, as by spraying,

or the dried pulp will be completely treated by dipping. The sheet thus treated with a water solution of a glycol ether compound will be redried using such heat as may be practically required. In such method of application it is believed that the reactivation is brought about at least in part by the rewetting of the sheet with the water and that one function of the agents is to prevent or minimize loss during the second drying of the improved activity obtained by the rewetting operation. However, where possible it will be economically preferable to carry out the treatment with the glycol ethers during the original drying on the sheet forming machine so that rewetting and redrying will be unnecessary.

The effective proportion of the glycol ether compounds incorporated in the wood pulp during the production of dry pulp from a wet slurry or in any reactivation treatment is from 0.02 to 0.5% based on the bone dry pulp.- Above this range in general no additional advantages are obtained and there are disadvantages in that the pulp sheet will tend to become undesirably soft and dusty and will give a final product undesirably contaminated. i i

We find that sheet wood'pulp dried in the presence'of the agents of the invention has markedly improved acetylation reactivity as compared with pulp dried in a conventional manner in the absence of these additives. This may be demonstrated by the following convenient and rapid laboratory test for comparing the acetylation reactivity of samples of sheeted wood pulp fibersz" Small specimens of the pulps to be examined are dampened with distilled water or with solutions of the agents of the invention and dried in a circulating oven at a selected controlled elevated temperature to, place them in an initially comp-arable condition. An accurately weighed sample of 0.5 gram of this pulp is torn into small bits and placed in a 35 ml. vial. A flattened glass rod is placed in the vial through a hole in the cap and thevial and sample set in a water bath at20 C. V

The acetylating mixture is prepared by mixing 2.500 .gms. H2804; 88.0 ml. acetic anhydride, and 175.0 ml. acetic acid. This mixture is unstable and should be freshly prepared every two days. 7

To the sample vial in the water bath 15 ml. of the acetylating mixture are added from a pipette. The pulp and acid are mixed with the glass rod, which remains in the vial. The vials are stored in the water bath and the mixing repeated every 15-20 minutes. It is important to include a standard sample with each group of unknowns and to handle and agitate all samples alike.

' lots were tested by the above procedure after treatment Thus application is made largely with solutions of various glycol ether compounds. The dry pulp samples were treated with approximately 0.4% by weight of the agents, by dipping in water solutions, and were redried at 50 C. The applied comp ounds and test observations are shown in the following Table I; The effect of the initial machine drying is also shown by a sample which was given no laboratory pretreatment at all and by others taken from the commercial producs tion-prioi to machinedrying and dried attwotemperatures in the laboratory.

TABLE I Acetylation reactivity of acetate woodpulps'treated with alkyl glycol ether compounds Acetylation Results 'Test'series Laboratory Treatment and Agent'Applied 1 Dissolv- Appearance ing Time, of Solution No laboratory treatment" 8-10 Many fibers. I'Mach2"ne Dried water only 7 gg Acetate Puzp' Diezgiylene glycol butyl 5 D0.

' e er.

Water only 7 Clear, many fibers. Diethylene-glyeol n-butyl. 5. 5 Clear, few ether. fibers. Dietlgglleiilel glycol 2'-ethyl- 5.5 Do. II-Machine u 8 .DriedAcetate' Dgefitiheyrlene glycol ethyl 7 Do. PulP- Ethylene glycol ethyl 7 Do. ether. Ethylene glycol butyl 7 Do. ether. Ethylene glycol phenyl' 7 Do. e er. III=-Acetate PuZp Dried only, at 25 C 5. 5' Clear.

.52; furiously Dried only, at 85 C 10-12 Opaque.

1 In series I and II 0.4% of agent on dry basis was applied where agents agessgeified and the pulp treated thus or with water as a control re-dried 8 The sheet wood pulp treated prior to completion of drying with the agents of the invention has also markedly improved properties when usedin aqueous reaction processes, particularly those involving a mercerizing step as in the viscose process; In these aqueous processes the treated pulp sheets are wetted more rapidly by water or NaOI-I solutions, in the case of the latter giving more uniform mercerization. This may be demonstrated by the following rapid test for comparing the absorbency of sheets of dried pulp.

Absorbency is determined by allowing a drop of water orNaOH' solution to fall on the pulp sheet from a height of 1 to 2' cm. and measuring the time required for the disappearance of free liquid on the surface of the sheet.

A series of samples tested by this-method is shown in Table II. The samples Were given various treatments prior to 'testing, as shown in the table.

TABLE II Absorbency of wood pulp sheets treated withvalkyl glycol ether compounds The above data show the increasing resistance to absorption resulting from further drying of the pulp sheets. at an elevated temperature, and the greatly improved absorptivity following, treatment with the agents of the invention, even after excessive drying.

This beneficial efiect in the mercerizing process of the glycol ether compounds'as herein incorporated in the pulp is'notabiy different from the effect in similar circumstances of normal so-called surface-active agents, which generally do not causesuch improved absorptivity or penetration 6 in the pulp: after excessive drying, particularly-in: caustic soda' solutions.

When alkali cellulose prepared: by the improved mercerizing process of the invention is utilized in the viscose rayon process, certain further improvements are effected in the subsequent steps of xanthating, dissolvingandfiltering. In viscose solutions there is usually a certain amount of undissolved fibers and gel-like material due .to the incomplete reaction of the cellulose with the carbon bisulfide during xanthation. Prior to spinning, the viscose solutions are filtered several times to remove these gels and undissolved fibers. In the event that the viscose solutions contain excessive amounts of undissolved and partially-dissolved fibers, filtration is an expensive operation. In such cases the filtersbecome rapidly clogged and the filter media must be changed frequently in order that the viscose will pass through in a reasonable time; Frequent changing of the filter media is expensive, not only as regards consumption of 'filter cloth but also in iew of the very considerable amount of labor involved and also since a certain amount of viscose is lost" every time the filter is opened up. Furthermore; when the viscose solutions contain very large proportions of gel-like material, filtration is usually not altogether satisfactory in that some of the smaller gel-like particlestend' to pass through the pores of the cloth with adverse efiect upon the spinning operation.

It has heretofore been the practice in the viscose industry, when processing pulps which tend to yieldviscose solutions high in undissolved material and having poor filtration properties, to minimize such difiiculties by carrying out the xanthation with amounts of carbon bisulfide considerably in excess of that normally required. Use'of excess carbon bisulfide is expensive and in addition is technically undesirable in' that it may adversely afiect certain properties such as the ripening of the viscose and yarn characteristics. We have found that when processing pulps-which have a resistance to penetration by caustic soda in the mercerizing'step; and which would normally tend to give poorly filtering viscose solutions, the addition of minute amounts of the glycol ether compounds to the pulp as heretofore described so improves the steeping operation that the alkali cellulose subsequently reacts. much more completely with carbon bisulfide and yields a viscose solution very free from undissolved and partially dissolved cellulose particles and having good filtration properties. This result can be accomplished not only without the use of excess carbon bisulfide, but in many cases satisfactory viscose-solutions can be. obtained using amounts of carbon bisulfide very substantiallyless than the amounts normally required.

When the glycol other compounds are incorporated in the wood pulp, by the pulp manufacturer, the pulpsheets come to the rayon manufacturer in a form calculated to secure the full advantages of the invention in the preparation and processing of the viscose into high grade rayon The following small scale laboratory test may be conveniently used to show the efiect in the viscose process of carrying out the mercerizing operation with pulp treated according to the invention.

A bundle of 10' .x 10" pulp sheets weighing approxi mately 650 gm. is steeped in caustic soda solution containing 18.5% NaOH and about 1.5% hemicellulosefor 30 minutes at 30 C., and then pressed to a weight of 2.70 times the original weight ofpulp. This mercerizing procedure is' carried out both with samples of pulp treated with glycol other compounds according to .the invention and with a control sample treated only with water and dried in the same manner as the treated samples.

The pressed sheets of alkali cellulose are shredded 60 minutes at 30 C. At the end of the shredding, the alkali cellulose is analyzed for percent NaOH" and percent cellulose. I

The shredded alkali celluloseis then placed in /2 gallon glass top fruit jarssealed with rubber rings and aged 24 7 to 48 hours at 30 C. under conditions predetermined to give viscose of about 35 seconds viscosity (time for A3" steel ball to fall '20 cm.) at the time it is subjected to testing- The aged alkali cellulose is then Xanthated in the glass jars using 31% CS2 based on cellulose in alkali cellulose and rotating the jars on rollers for 105 minutes at 30 C. The xanthate is mixed with caustic soda and water for 150 minutes at C. to give a viscose solution'with composition 8.5% cellulose and 5.25%NaOH'. I i

After standing 24 hours, at ,C., a filtration test is made on the viscose. In this filtration test a plugging value is determined by filtering through a standard cotton batting filter medium, taking rate measurement at increasing time increments. The .plugging value.is calculated by extrapolation from these measurements as the amount of viscose which would pass through one unit of filter area when the filter would be completely plugged. The higher the plugging value the better the'viscose. Under the standard conditions of the test the plugging value therefore indicates the relative reactivity 'of the pulp sample processed.

Samples of a type of low viscosity Wood pulp normally used in the manufacture of cellophane'were tested by the above procedure after treatment with several of the glycol ether compounds of the invention. The samples and the test observations are shown in the following Table III. The wood pulp sheets, dried on the manufacturing machine, wer'e later treated by spraying with a water solution of the agent named and redried at 50 C.

TABLE n1 Reactivity in viscose process of wood pulps treated with alkyl glycol ether compounds We claim:

1. As a new article of manufacture, relatively dry refined wood pulp in sheet form having incorporated therein a glycol ether compound having the formula R(OCH2CH2)OH where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a integer from 1 to 2.

'2. In the drying of refined wood pulp at an elevated temperature the improvement which comp-rises adding at benzyl group, and x is an astage prior to completion of drying from 0.02 to 0.50

percent by weight, based on the bone dry weight of the pulp, of a glycol. ether compound. having the formula mocmcnmon where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and x is an integer from 1 to 2. v

3; As a new article of manufacture, relatively dry refined wood pulp in sheet form having incorporated therein from 0.02 to 0.50 percent by weight, based on the bonedry .weight of pulp, having the formula V l Rocuzcrrzocmcmon where R is an aliphatic hydrocarbon radical with 4 to 6 of a glycol ether compound carbon atoms.

4. In the drying of refined wood pulp at an elevated temperature the improvement which comprises adding at a stage prior to completion of 'dryingjfrom 0.02 to 0.50

percent by weight, based on the bone dry weight of the pulp, of a glycol ether compound having the formula ROCHzCHzOCHCHzOH where R is an aliphatic hydrocarbon radical with 4 to '6 carbon atoms.

5. In the process of claim 2, the use of a glycol ether compound which is the n-butyl ether of diethylene glycol.

6. In the process of claim 2, the use of a glycol ether compound which is the 2-ethyl. butyl ether of diethylene glycol. V

7. In the acylation of refined'wood pulp driedlatan elevated temperature in .a substantially nonaqueous medium, in which substantiallydry wood pulp is acylated, the'improvement which comprises use in the acylation process of pulp in which there has been incorporated prior to completion of drying at an elevated temperature a glycol ether compound'having the formula V R(OCH2CH2)OH where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to' 6 carbon atoms, a phenyl group, and a benzyl group, and x is an integer from 1 to 2. V

8. In the processing of refined wood pulp dried at an elevated temperature into cellulose acetate, the improve ment which comprises use in the acetylation process of pulp in which there has been incorporated prior to com-v pletion of drying at the elevated temperature from 0.02.

to 0.50 percent by weight, based on the bone dry weight of pulp, of a glycol ether compound having the formula R( OCHzCHz) rOH where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and x is an R (OCHzCHz) 10H where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and x is an integer from 1 to 2.

10. In the processing of refined Wood pulp dried at an elevated temperature into cellulose acetate, the improvement which comprises use in the acetylation process of pulp in which there has been incorporated prior to completion of drying at .an elevated temperature from 0.02

a to 0.50 percent by weight, based on the bone dry weight of the pulp, mula of a glycol ether compound having the fornocrrcmbcmcmon compound which is the 2-ethyl butyl ether of diethylene.

glycol.

13. In the processing of refined dry wood pulp to form a cellulose derivative in which substantially dry wood pulp is mercerized in aqueous caustic soda solution, the'imk provement which comprises using in the mercerizing step wood pulp in which there has been incorporated prior to completion. of drying at an elevated temperature a glycol ether compound having the formula.

Where R is a hydrocarbon radical selected from the group consisting of an .alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and x is an integer from 1 to 2.

14. In the process of claim 13, the use of a glycol ether compound which is the n-butyl ether of diethylene glycol.

15. In the process of claim 13, the use of a glycol ether compound which is the 2-ethyl butyl ether of diethylene glycol.

16. In the procasing of refined dry wood pulp into rayon by the viscose process, the improvement which comprises carrying out the mercerizing step of the viscose process using sheets of substantially dry pulp in which there has been incorporated prior to completion of drying at an elevated temperature a glycol ether compound having the formula where R is a hydrocarbon radical selected from the group consisting of an alkyl radical with 1 to 6 carbon atoms, a phenyl group, and a benzyl group, and x is an integer from 1 to 2.

References Cited in the file of this patent UNITED STATES PATENTS 1,932,255 Sherrard et va1 Oct. 24, 1933 2,051,220 Malm et al Aug. 18, 1936 2,664,384 Richter et al Dec. 15, 1936 2,273,039 Hudson Feb. 17, 1942 2,362,217 Schlosser et al. Nov. 7, 1944 2,481,693 Schlosser et al Sept. 13, 1949 2,491,499 Katzen et al Dec. 20, 1949 2,538,457 Hudson Jan. 16, 1951 2,623,875 Schlosser et a1. Dec. 30, 1952 2,686,132 Gray Aug. 10, 1954 

1. AS A NEW ARTICLE OF MANUFACTURE, RELATIVELY DRY REFINED WOOD PULP IN SHEET FORM HAVING INCORPORATED THEREIN A GLYCOL ETHER COMPOUND HAVING THE FORMULA 